![]() They employed a mass spectrometer coupled to the gas outlet of the anode and monitored the m/ z value of 44 amu (atomic mass unit), which is related to CO 2. 19 by including the CO 2 mass balance within the anode channel. 21 modified the model proposed by Zhang et al. They raised the possibility that either χ COĭid not in fact oscillate or the resolution of the gas analyzer was too low for the oscillatory frequencies evaluated. To verify if the anodic CO concentration oscillates simultaneously with the overpotential, the authors used an on‐line infrared gas analyzer however, they did not observe oscillations in the CO concentration at the anode outlet stream. ![]() Kept constant, the model still exhibited oscillatory behavior. ) at the anode outlet was considered not to be essential for the occurrence of oscillations, that is, even with χ CO However, the temporal dependence of the molar fraction of CO ( χ CO 19 in 2004 demonstrated the relationship between the anodic overpotential and the CO ad coverage, and also showed that OH ad and H ad coverage are essential variables for the occurrence of oscillations. 17, 23, 24, 25, 26, 29, 30, 31Īn interesting way to study the reaction mechanisms involved in such systems is by combining the results of potential variation over time with another technique, such as on‐line mass spectrometry (OLMS). In fact, it has been reported that operating a fuel cell under an oscillatory regime can result in higher average power densities than those obtained at a steady state. 13, 14, 15 In addition, oscillatory dynamics in a PEMFC are not restricted to systems with a Pt‐Ru/C anode, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28 and the occurrence on Pd‐Pt/C 29 and on Pt 30, 31 anodes has also been reported.įrom a technical point of view, the occurrence of oscillatory kinetics can be thought of as an autonomous self‐cleaning process 32 that can prevent the anode becoming completely poisoned by adsorbed carbon monoxide, as is the case under conventional, non‐oscillatory conditions. 11 An interesting aspect of these devices is that the reactions that occur on the surface of these catalysts and the adsorption/desorption processes are interrelated through the anode potential, and this delicate interplay can result in oscillatory behavior. 2, 5, 6, 7, 8, 9, 10, 11, 12 Within the possibilities of bimetallic electrocatalysts, Pt‐Ru shows great activity for H 2 oxidation in the presence of CO and it is the most successful alloy characterized to date. 2, 3, 4, 5 Strategies inspired by the use of a second metal in Pt‐based anode catalysts have been explored as potential routes to increase the CO tolerance relative to pure Pt. ![]() 1 Even very low concentrations of carbon monoxide in the anode fuel can result in a severe decrease in energy conversion efficiency. In the case of hydrogen, an important limitation is the source of hydrogen used because when hydrogen is generated by hydrocarbon reformation, CO is produced concomitantly and remains as a contaminant. Polymer electrolyte membrane fuel cells (PEMFCs) are devices that convert the chemical energy of hydrogen or other fuels and oxygen directly into electrical energy. By using CO stripping, we also discuss how the onset of CO oxidation is related to the maximum overpotential reached during a cycle, whereas the minimum overpotential can be associated with the catalytic activity of the electrode for H 2 oxidation. For both anodes, it has been observed that, in general, an increase in current density implies an increase in oscillatory frequency. This fact is consistent with an autonomous adsorption–oxidation cyclic process. Overall, we observed that oscillations in the anodic overpotential are in phase with that of the CO and CO 2 signals. ![]() We used on‐line mass spectrometry to investigate how the mass fragments associated with CO 2 and CO ( m/ z 44 and 28, respectively) varied with the voltage oscillations. Herein we report experimental studies of voltage oscillations that emerge in a PEMFC equipped with a Pd/C or PdPt/C anode and fed with H 2 contaminated with CO (100 ppm). The self‐organization of the anodic overpotential is interesting because it can be accompanied by an increase in the average performance. Polymer electrolyte membrane fuel cells (PEMFC) fed with H 2 contaminated with CO may exhibit oscillatory behavior when operated galvanostatically. ![]()
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